The present invention relates to an apparatus for separating a target gas from a mixture of at least two gases. More particularly, the invention relates to such an apparatus which employs an activated carbon or graphitic foam monolith to adsorb the target gas from the mixture of gases and thereby separate the target gas from the mixture.
Gas filtration or separation devices are used to separate a target gas from a gas stream containing a mixture of gases. These devices commonly employ an adsorbent material, such as zeolite or activated carbon, to adsorb the target gas from the gas stream. Once the adsorbent becomes saturated with the target gas, the target gas is desorbed from the adsorbent using, for example, thermal or electrical energy and discharged into a storage container. The quantity of target gas that can be separated by the device depends on the amount of adsorbent used and the number of adsorption and desorption cycles the adsorbent undergoes.
The rate at which the target gas may be adsorbed onto the adsorbent is directly related to the temperature of the adsorbent. Thus, the lower the temperature of the adsorbent, the quicker the target gas will be adsorbed. However, as the target gas is adsorbed onto the adsorbent, a substantial amount of heat is generated which can raise the temperature of the adsorbent and its supporting structure by a significant degree. In addition, when heat is used to desorb the target gas from the adsorbent, this heat can substantially raise the temperature of the adsorbent and its supporting structure. Therefore, the heats of adsorption and desorption must be dissipated from the adsorbent both prior to and during each adsorption cycle.
Thus, the ability of prior art gas separation devices to execute repeated adsorption and desorption cycles depends in large part on the thermal conductivity of the adsorbent. When the thermal conductivity of the adsorbent is limited, sufficient time must be allowed both prior to and during the adsorption cycle to permit the heats of adsorption and desorption to be dissipated from the adsorbent. This in turn usually requires the use of a large amount of adsorbent in order to separate an acceptable amount of target gas during each adsorption cycle. Moreover, although the cycle times can be decreased somewhat by the use of ancillary heat removal devices, such as cooling tubes and fins, these devices increase the expense and complexity of the apparatus.